Sonny Liston of course. You have to put the older George Foreman jab up there as well. Miguel Cotto and the Mike Tyson of old before Don King came in the picture. The Tyson that had Cus, Rooney, and Torres in his corner.

In the game today id go with Miguel Cotto, he busts guys up with that jab, Cotto throws the jab like a jab Should be thrown - as a weapon and not just a range finder! He's dropped guys with it like Gomez and Clottey, Boom its like a pole fireing out at u which comes from his strong hand of course as he is a converted southpaw

Wlad Klitchko breaks hearts and faces his with his long jab

All time, Bazooka Quartey had a piston of a jab and would win fights off of the back of that shot alone

Sonny Liston is the obvious shout

Lennox Lewis had a heavy jab when he threw it with purpose (whichhe didnt always do)

If we're just sticking to heavyweights then Wlad and Lennox obviously spring to mind. Lennox was literally stopping a 245lb man in Vitali dead in his tracks with the jab alone. He ripped guys faces up with it. Just an incredibly heavy and powerful jab. Wlad's jab is more snappy, and he doesn't put his weight into it so much, but it obviously has a devastating effect on his opponents, causing them to shell up after a few rounds. Comeback Foreman's jab was incredibly heavy, like a telephone pole ramming into guys' faces. Likewise Mercer (a very underrated jabber). Bruno's jab was very heavy as well, coming as it did from those broad bodybuilder's shoulders. Rahman might not be up there, but he deserves a mention too.